The present invention relates to a new and improved construction of apparatus for circulating and/or aerating a liquid, especially waste water located in a basin or tank, by means of a centrifugal impeller or rotor immersable in the liquid and rotatable about a substantially vertical axis, said centrifugal impeller being equipped with a multiplicity of at least approximately radially extending liquid conveying channels, and furthermore, this invention relates to the use of the aforesaid apparatus.
It is already known to the art to circulate waste water which is to be aerated by means of an impeller or rotor located below the level of the liquid located in an activation tank or activated-sludge basin. The impellers used for this purpose are generally all constructed in a manner such that the liquid conveyed through the impeller departs in horizontal direction at the periphery of the impeller. However, with regard to flow considerations this is quite unfavorable, since the liquid emanating from the liquid conveying channels should be guided upwardly or downwardly along the wall of the tank or vessel in order to realize the desired flow path. However, if the liquid emanating from the rotor flows in a horizontal direction perependicularly towards the wall of the tank or basin, there is not realized any exactly defined flow in the desired direction. However, if there are arranged flow deflection means at the basin wall, then such tend to become markedly coated with sludge and in the case of large tanks or basins result in a considerable increase in the construction cost.